About the LBT Project
Version: 31 August 2002
The Large Binocular Telescope (LBT) is a collaboration between the Italian astronomical community (represented by the Instituto Nazionale di Astrofisica (INAF)), The University of Arizona, Arizona State University, Northern Arizona University, the LBT Beteiligungsgesellschaft in Germany (Max-Planck-Institutfür Astronomie in Heidelberg, Landessternwarte in Heidelberg, Astrophysikalisches Institut in Potsdam, Max-Planck-Institut für Extraterrestrische Physik in Munich, and Max-Planck-Institut für Radioastronomie in Bonn), The Ohio State University, Research Corporation in Tucson, and the University of Notre Dame. The goal of the LBT project is to construct a binocular telescope consisting of two 8.4-meter mirrors on a common mount. This telescope will be equivalent in light-gathering power to a single 11.8 meter instrument. Because of its binocular arrangement, the telescope will have a resolving power (ultimate image sharpness) corresponding to a 22.8-meter telescope. The feasibility study for the project was completed in early 1989. In 1992, the original partners (Arizona, Italy and Research Corporation) decided to proceed to the construction phase even though the funds available were sufficient only to complete a "reduced first light" telescope with only one primary mirror in place. With the addition of LBTB and Ohio State University to the consortium in 1997, the project began to construct the full binocular telescope. The telescope was completed in Italy and shipped to Arizona in the summer of 2002.
The Large Binocular Telescope Corporation was established in 1992 to undertake the construction and operation of the LBT. The LBT Corporation Board of Directors oversees the project, which currently includes two representatives from Arizona, Italy, and LBTB, and one representative from Ohio and Research Corporation.
The present members of the Board are:
Treasurer of the Board: Joel Valdez
The LBT Corporation maintains one Corporate Office and two Project Offices. The Corporate Office is located in Tucson, Arizona. It handles the financial management of the corporation and the communications with board members.
The two Project Offices are located in Tucson, Arizona and in Arcetri, Italy. The Project Offices oversee the design and construction activities of the telescope. Monitoring the daily operations and providing management of the project are:
The LBT Project Office in Tucson coordinates contractual agreements and financial functions.
A contract for the detailed mechanical design of the telescope was signed in April of 1994 with a Consortium formed by the Italian engineering firms of ADS International (Lecco) and European Industrial Engineering (Mestre). The two companies provided quality assurance monitoring during the manufacturing, assembling, and testing of the various sub-systems as well as during the telescope pre-erection in the workshop. In January 1998, a contract was awarded to Ansaldo Energia S.p.A. (Milan) for the fabrication and factory pre-erection of the main structure of the telescope. The telescope was shipped to Arizona in mid-2002. The Hydrostatic Bearing System and Gears for the telescope were manufactured by Tomelleri S.r.l. in Verona, Italy.
The Large Binocular Telescope is part of the Mt. Graham International Observatory near Safford, Arizona. The construction of the observatory with three telescopes was approved by Congress in November 1988. During the 1996 construction season, the site for the LBT telescope on Emerald Peak was cleared of trees and rocks and a retaining wall was erected along the northeast side. Geological surveys were performed to identify the best location for the telescope pier, and the foundation was poured just before the arrival of inclement weather. During the 1997 season, the telescope pier and ring wall that supports the rail of the rotating upper part of the enclosure were constructed. Steel for the lower portion of the enclosure was erected, and the 200-meter utility trench was begun. The 1998 season included the erection of the rail and bogies, the rotating building structure, and cladding of the lower enclosure. The 1999 season included completion and cladding of the rotating building structure, installation of the pier cap and the completion of the utility trench. Contracts for enclosure completion packages (architectural finishing, HVAC and plumbing mechanisms, and electrical systems and controls) were signed and work began in 1999. The enclosure was completed by the end of 2002.
Contracts for the fabrication and polishing of the two 8.4- meter primary mirrors are in place with The University of Arizona Steward Observatory Mirror Lab. The Lab has already successfully cast and polished three 6.5-meter honeycomb mirrors in its program of casting large mirrors. Casting of the first 8.4 meter honeycomb mirror took place in mid-January 1997. The mirror underwent a slow annealing and cooling process and was inspected in early April confirming that the leakage of glass noted during the casting resulted in some thinning of the mirror's faceplate. An area consisting of approximately 10% of the total surface of the mirror was at a less than optimum thickness. Two tons of glass were added to the mold in late April and a slow heating process was started. The faceplate was remelted in June, and the mirror was annealed and cooled during the summer. In September 1997, the furnace was opened to reveal a 100% successful casting. The mirror was lifted in February 1998, and the mold material has been washed out. Finishing of the back side of this mirror was completed in June 1999. Casting of the second primary mirror took place in May 2000. With additional tension on the Inconel bands, no glass leaks occurred during this casting. As of August 2002, the first mirror is being polished and the second mirror is being cleaned out.
The detailed architectural design of the enclosure was done by a Consortium of companies headed by M3 Engineering & Technology Corp (M3). M3 has already designed many telescope enclosures including others on Mt. Graham, and has been able to provide the necessary knowledge on the local building codes and regulations. ADS (also part of the Consortium) provided continuity in the enclosure design evolution since it has been working on the project since 1985. ADS and EIE were charged with assuring the correct interface between the enclosure and the telescope design contract. Hart Construction Management Services of Safford, Arizona is the General Contractor.
Substantial progress has been made at the Steward Observatory Mirror Lab on a facility to both polish and test secondary mirrors. Polishing of the Sloan Digital Sky Survey convex secondary was completed in October 1996. The MMT F/9 secondary was aspherized in the fall of 1996 and the MMT F/5 was aspherized in 1997. The MMT F/9 secondary completed final polishing with the stressed lap in 1998. The MMT F/15 adaptive shell completed final polishing in 1999. The 2.5-meter illuminator mirror to be used for testing the LBT F/4 and MMT F/5 secondaries has been purchased and was polished by Rayleigh Optical.
ADS International finished the final design for the bell jar to be used during the aluminizing process of the primary mirrors. A contract for the fabrication of the bell jar along with the mirror cells was awarded to Ansaldo Energia S.p.A. in January 1998. Integration of the bell jar will be carried out at The Ohio State University.
The partners: The University of Arizona, INAF, the LBT Beteiligungsgesellschaft, The Ohio State University and Research Corporation have committed sufficient funds, $87,800,000 ($1998), to permit construction of the complete telescope and enclosure with two sets of optics and instrumentation. The project is proceeding with construction on that basis.
Current schedules for the telescope, mirror and enclosure suggest that first light will occur in the spring of 2004. The second primary should follow approximately 1 year later.
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The telescope will use two 8.408 meter, F/1.142 primaries to provide a collecting area equivalent to an 11.8 meter circular aperture. Included in the $88.8 million budget are the costs for two adaptive F/15 secondaries. Other focal stations and features considered scientifically important for future expansions will be included in the optical and mechanical design of the telescope but not initially implemented.
The two parabolic primary mirrors have been fabricated at the Mirror Laboratory located in the campus of The University of Arizona in Tucson, Arizona. Each of the F/1.142 honeycomb borosilicate mirrors weighs approximately 16 metric tons and was made utilizing E6 glass manufactured by Ohara in Japan. The finished mirror diameter is 8.417 meters.
The principal focal stations of the telescope will be:
(b) phased combined, re-imaged F/15, center
2. TELESCOPE STRUCTURE
The telescope is an elevation over an azimuth mounting. The optical support structure moves on two large C-shaped rings and the compact azimuth frame transmits the loads directly down to the pier. The two 8.4 meter (331 inch) diameter primary mirrors are mounted with a 14.4-meter center-center separation. By using swing arms to rotate the secondary and tertiary mirrors and their supports, it is possible to switch the telescope from one mode of observation to another very quickly. The short focal length of the primary mirrors (F/1.14) permits a compact, and therefore quite stiff telescope structure.
3. TELESCOPE ENCLOSURE
The enclosure design has been driven by the following requirements. Various combinations on these requirements resulted in convergence on the concept described below:
Following are some of the major design features of the LBT project enclosure design.
The basic design of the building is a corotating box around the telescope that sits on a circular pier. The structural steel was fabricated and erected by Schuff Steel in Phoenix, AZ. Siding for the rotating building was installed by EMCO of Sacramento, CA.
The rotating building rides on a 23-meter diameter circular rail held above the ground by a reinforced concrete wall. The rail was manufactured by Fravit S.r.l. in Lecco, Italy, and was installed in spring, 1998. The four bogies that ride on this rail were manufactured by Costameccanica S.p.A. in Lecco, Italy.
Each aperture of the binocular telescope has a 10.4-meter wide aperture for viewing. These two apertures are covered by sliding shutters which move apart laterally to open the slits. Additional openings on the back and sides allow wind ventilation to flush the building. When the wind is strong, a windscreen can be raised to protect the telescope from buffeting.
55 ton crane
A 55-ton crane will allow handling of large equipment through a 4x10 meter hatch in the telescope floor. Both the aluminizing bell jar and the mirror cleaning system will be transferred from the floor of the auxiliary building to the telescope floor through the hatch. A second crane is available to handle equipment at ground level. These cranes were manufactured by Lario Impianti S.r.l. in Osnago, Italy.
The main telescope building will house all the machinery and equipment needed to operate the telescope, the control rooms for the astronomers and some living quarters.
An auxiliary building will surround the telescope from the northwest to the northeast side. It will provide space for the optical, electrical and mechanical laboratories where astronomical instrumentation can be readied and repaired if necessary. The bell jar and the aluminizing equipment will also be stored there.
An elevator, located inside the telescope pier, provides access to the various fixed levels and the transfer floor to the rotating building. A second elevator in the rotating building will provide access to the various levels of the telescope.
The LBT Scientific Advisory Committee (SAC) has developed the following list of observational priorities (in no particular order) to guide the telescope design.
The SAC envisions the following list of facility instruments, which will be implemented on the baseline telescope.Interferometric imager
Faint object optical spectrograph
Near infrared camera and spectrograph